Electron beam inspection: CDU dual-mode inspection and lithography ghost image detection

Abstract

For a recent replacement metal gate (RMG) FINFET technology using an SOI substrate, two cases are reviewed using CD uniformity (CDU), a high throughput CD measurement technique using an e-beam inspection tool. In the first case, a CD is measured in the same process tooling as the defect inspection. The SRAM gate CD is shown to correlate strongly with defectivity, which affects the RMG formation. In this FINFET technology, the high aspect ratio of the gate makes removing the dummy gate very difficult. Residue is left behind, especially in multi-fin structures. The CD variation across wafer is shown, and inversely correlates with the observed defect density. In the second case, CDU is used to confirm and validate the fix for a latent-image ('ghost image') yield issue.